1. Field of the Invention
The present invention relates to soft-magnetic FeCo based target materials which have superior atmospheric corrosion resistance and magnetic properties.
2. Description of Related Art
In recent years, there have been remarkable progresses in magnetic recording technology, and heightening record densities in magnetic record media is proceeding due to increasing drive capacities. In magnetic record media for longitudinal magnetic recording systems currently used worldwide, however, attempts to realize high record densities result in refined record bits, which require high coercivity to such an extent that recording cannot be conducted with the record bits. In view of this, a perpendicular magnetic recording system is being studied as a means for solving these problems and improving record density.
The perpendicular magnetic recording system is a system in which a magnetization-easy axis is oriented in the direction vertical to a medium surface in the magnetic film of a perpendicular magnetic record medium, and is suitable for high record densities. In addition, as for the perpendicular magnetic recording system, a two-layered record medium has been developed having a magnetic record film where record sensitivity is improved and a soft-magnetic film. CoCrPt—SiO2 alloys are generally used for this magnetic record film.
Examples of known soft-magnetic layers are as follows. Japanese Patent Laid-Open Publication No. 2004-346423 proposes an Fe—Co—B alloy target material in which the diameter of the maximum inscribed circle which can be drawn in a region with no boride phase in a cross-microstructure is equal to 30 μm or less. Japanese Patent Laid-Open Publication No. 2005-320627 proposes a CoZrNb and/or CoZrTa alloy target material which restricts variations of soft-magnetic films formed by sputtering and achieves a reduction in particles produced in the sputtering process.
It is known that FeCo based alloys comprising Fe and about 35 at. % Co have the highest saturation magnetic flux density. For example, U.S. Patent application Publication No. 2002/0058159 proposes a soft-magnetic film made of a boron (B)-doped alloy comprising Fe and 35 at. % Co.
Magnetron sputtering methods are generally used for preparation of the aforementioned soft magnetic films. This magnetron sputtering method is a method in which a magnet is disposed behind a target material to leak the magnetic flux onto a surface of the target material for converging plasma in the leaked magnetic flux region, thus enabling a high-speed coating. Fe-based materials are desired since high magnetic flux density is required for a soft-magnetic film made of a target material used for the magnetron sputtering. In this case, however, there are problems that corrosion resistance is unsatisfactory, that oxidation of the target material degrades film quality, and that abnormal discharges occur in the oxidized area during the sputtering process to result in sputtering failure.